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Dr.Naresh Kumar
Junior Resident
Dept. of Pulmonary Medicine
AnAtomy of pleurA…
Definition and layers of Pleura
Surface marking
Recesses of pleura
Blood supply
Lymphatic drainage
Nerve supply
Definition and layers of
• Pleura
• Serous membrane that covers the lung parenchyma,
mediastinum, diaphragm and the rib cage.
• It comprise visceral and parietal layer.
Visceral pleura
– Covers the lung parenchyma, not only at its point of contact with
chest wall, diaphragm and the mediastinum but also in the
interlobar fissures.
– It apposed to lungs and cannot be dissected from the surface.
• Endo pleura :
 Most superficial layer
 Composed of a continuos layer of mesothelial cells
 External elastic layer (chief layer)
 Consist of thin layer of dense collagen and elastic tissue
 Responsible for pleural mechanical stability
 Vascular layer (interstitial layer)
 Consist of connective tissue containing lymphatic and blood
 Continuos with the interstitial tissue of the interlobular septa and
directly overlies the lobular-limiting membrane.
Parietal pleura
– It lines the thoracic wall.
– Covers the inner surface of rib cage, mediastinum and
– It extends into the root of neck to line the undersurface
of suprapleural membrane at thoracic outlet
According to intrathoracic surface it lines :-
Cervical pleura
Costal pleura
Diaphragmatic pleura
Mediastinal pleura
• Cervical pleura :
– “pleural capula” or dome of pleura.
– It extends from the superior thoracic aperture into the
root of neck, forming a cup shaped pleural dome over
the apex of lung.
– The cervical pleura at higher levels in infants and young
children because of the shortness of their necks, thus
more prone to injury.
– The small areas of pleura exposed in the costo vertebral
angles inferiomedial to the 12th ribs are posterior to the
superior poles of kidneys. More prone to injure during
surgical procedure in posterior abdominal wall.
• Costal pleura :
– It covers the internal surface of :
Intercostal spaces
Back of sternum
Costal cartilages
Sides of vertebral bodies
• Mediastinal pleura :
– It covers the lateral aspects of the mediastinum.
– It is attached to blood vessels and bronchi that
constitute the lung root.
• Diaphragmatic pleura :
– Covers the superior or thoracic surface of diaphragm on
each side of mediastium.
– In quite respiration the costal and the diaphragmatic
pleura are in apposition to each other.
– They separate in deep inspiration.
Pleural cuff
 The two layers, parietal and visceral, continuous with
one another by means of a cuff of pleura.
 This cuff surrounds the structures entering and
leaving the lung at the hilum of each lung.
 Pleural cuff hangs down as loose fold called the
pulmonary ligament.
 Fold contains a thin layer of loose areolar tissue with a
few lymphatics.
It provides a dead space into which the pulmonary veins can
expand during increased venous return.
Embryology of pleura
• Pleural cavity :
– Derived from the coelomic cavity (body cavity)
– Coelomic cavity divided into pericardium, pleural cavities and
the peritoneal cavity through the development of three sets of
portions :
Septum transversum : serves as an early partial diaphragm.
Pleuro pericardial membranes : divide pericardial and pleural
Pleuro peritoneal membranes : unite with the septum transversum
to complete the partition between each pleural and peritoneal cavity.
– Pleural cavity is fully lined by mesothelial membrane, the
 Visceral pleura :
 Primordial lung buds grows and bulge into right and left
pleural cavities, carry along lining mesothelium which
becomes visceral pleura.
 Parietal pleura :
 Lining mesothelial of pleural cavity becomes parietal
• Grossly, normal pleura is a smooth, glistening,
semitransparent membrane.
• Light microscopy, pleural consist of five layers :
– Mesothalial layer
– Connective tissue layer
– Superficial elastic layer
– Loose subpleural connective tissue layer (rich in vessels,
nerves and lymphatics)
In pleural fibrosis connective tissue is arranged in a coarse, basket
weave pattern and contains only a few capillaries.
– Deep fibroelastic layer (in continuity with the parenchymal
structures of lung, diaphragm or the thorax)
Mesothelial layer
• Single cell layer
• Different shaped cells – flattend or cuboidal or
6-12mm thickness
Microvillae present to decrease friction
Stomata present between the mesothelial cells that
communicate directly with lymphatic lucanes.
Capable of transformation into macrophages.
In a rheumatoid pleuritis, normal mesothelial cell
covering absent, instead there is pseudostratified layer
of epitheloid cells that focally forms multinucleated
giant cells .
Surface marking
Recesses of pleura
 There are two folds or recesses of parietal pleura which
acts as reserve space for the lung to expand during
deep inspiration.
 Costomediastinal recesses
 Costodiaphragmatic recesses
Costomediastinal recesses
 Are situated along the anterior margins of pleura.
 They are slit like spaces between the costal and the
mediastinal parietal pleura.
 Seperated by a capillary layer of pleural fluid.
 During inspiration and expiration, the anterior
borders of the lungs slide in and out of the recesses.
Costodiaphragmatic recesses
• Are slit like spaces between the costal and
diaphragmatic parietal pleura.
Separated only by a capillary layer of pleural fluid.
During inspiration, the lower margins of the lung
descend into the recesses.
During expiration, the lower margins of the lung
ascend so that the costal and the diaphragmatic pleura
come together again.
First part of pleural cavity to be filled up by pleural
It has capacity upto 300 ml.
Blood supply
• Arterial supply :
– Parietal pleura :
Costal pleura : small branches of intercostal arteries
Mediastinal pleura : supplied by pericardio phrenic artery
Diaphragmatic pleura : supplied by superior phrenic and
musculophrenic artery.
– Visceral pleura :
Bronchial artery : supplies visceral pleura facing the
mediastinum, pleura covering the interlobular surface and
part of the diaphragmatic surface.
Pulmonary artery : supplies remaining portion.
 Venous drainage :
 Parietal pleura
Through the intercostal veins which empty into inferior
venacava or brachio-cephalic trunk.
 Visceral pleura
Through pulmonary veins.
 Applied anatomy : Aspiration of any fluid from the
pleural cavity is called parencentesis thoracis. It is
usually done in the 6th intercostal space in the
midaxillary line. The needle is passed through the lower
part of the space to avoid injury to the neurovascular
Nerve supply
• Parietal pleura :
– Sensitive to pain, temperature, touch and pressure.
 Costal pleura : innervated by segmental intercostal nerves.
 Peripheral part of diaphragmatic pleura : innervated by
lower 6 intercostal nerves.
pain is percieved in adjacent chest wall.
 Central portion of diaphragmatic pleura and
mediastinal pleura :
innervated by phrenic nerve.
Pain is percieved in ipsilateral shoulder.
• Visceral pleura :
– Insensitive to common sensation such as pain and
– Sensitive to stretch.
– Innervated by autonomic nerves from the spinal
segments T4 and T5.
• Presence of pleuritic chest pain indicates
inflammation or irritation of parietal pleura.
Applied anatomy :
 Intrapleural anaesthesia :it is infusion of small volume
of local anaesthetic agent into the intrapleural space
through catheter. It diminish the pain sensation from
the area by action on intercostal nerves, indicated in
thoracotomy and insertion of chest drainage
Lymphatic drainage
• Parietal pleura :
– Costal pleura :
Ventrally : towards nodes along the internal thoracic artery.
Dorsally : towards the intercostal lymph nodes.
– Medistinal pleura :
Drain to tracheobronchial and mediastinal nodes.
– Diaphragmatic pleura :
Drain to parasternal, middle phrenic and posterior
mediastinal nodes.
• Lymphatic vessels in parietal pleura are in
communication with the pleural space by means of
• Stoma :
– 2-6 mm in diameter
– Round or slit like opening
– Found mostly on the mediastinal pleura and on the
intercostal surfaces.
– More stoma in the area where the mesothelial cells are
cuboidal rather then flat.
• Lacunas :
– Lymphatic vessels in parietal pleura have many
branches, some submesothelial branches have dilated
lymphatic space called lacunas.
• Stomas are found only over lacunas.
• Significance : Stomas with their associated lacunas
and lymphatic vessels are main pathway for
elimination of particulate matter from pleural space.
This transport system may provide a mechanism for
migration of malignant cell to distant organs in
patients with positive pleural lavage cytology.
• Visceral pleura :
– They have abundant lymphatic vessels.
– Lymphatics form a plexus of inter communicating
vessels that run over the surface of lung towards the
– It also penetrate the lungs to join the bronchial lymph
– Lymphatic vessel in visceral pleura have one way valves,
directing flow towards the hilum of lung.
– No stomas are seen in visceral pleura.
Physiology of pleura
 Pleural pressure
 Pleural fluid
 Pleural effusion
 Therapeutic application of pleural space
 Clinical condition associated with pleura
Pleural pressure
 It is pressure within the pleural space.
 It is pressure at the outer surface of the lung and heart,
and inner surface of thoracic cavity.
 With the chest closed and the patient relaxed, the
respiratory system is at its functional residual capacity
(FRC), which is approximately 35% of the total lung
capacity. Thus, at FRC, the opposing elastic forces of
the chest wall and lung produce a negative pressure
between the visceral and the parietal pleura, which is
called the pleural pressure.
 Significance :
 Because the lung, the heart, and the thoracic cavity are
all distensible, and because the volume of a distensible
object depends on the pressure difference between the
inside and the outside of the object and its compliance,
pleural pressure plays an important role in determining
the volume of these structures.
 Pleural liquid pressure
 pressure measured using fluid-filled catheters
 1.0 cm H2O/cm vertical height.
 It represents the pressure that influenced the absorption
of fluid.
 Pleural surface pressure
 pressure measured using surface balloons or suction
 0.3 cm H2O/cm vertical height.
 It represents the balance between the outward pull of
the thoracic cavity and the inward pull of the lung.
 Direct methods
measured by inserting needles, trocars, catheters, or balloons
into the pleural space.
Highly risk of producing a pneumothorax or of introducing
infection into the pleural space.
 Indirect methods
measured by a balloon positioned in the esophagus.
esophagus is a compliant structure situated between the two
pleural spaces, esophageal pressure measurements provide a
close approximation of the pleural pressure.
 Precaution to be taken –
 volume of air within the balloon must be small, so that
the balloon is not stretched and the esophageal walls are
not displaced; balloon must be short and
 balloon must be placed in the lower part of the
 Pleural pressure is not uniform throughout the pleural
 pleural pressure being lowest or most negative in the
superior portion and highest or least negative in the
inferior portion.
 factors responsible for gradient
 gravity,
 mismatching of the shapes of the chest wall and lung,
 weight of the lungs
 The magnitude of the pleural pressure gradient
appears to be approximately 0.30 cm H2O/cm vertical
 Significance of gradient :
 alveolar pressure is constant throughout the lungs, thus,
higher pressure gradient at the apex of the lung is
thought to be responsible for the formation of pleural
blebs at the apex of the lung.
 It also play a role in difference in ventilation at apex and
base of lung.
Pleural fluid
 Fluid present between the parietal and visceral pleura,
the pleural space is called pleural fluid.
 Fluid act as lubricant and allows the visceral pleura
covering the lung to slide along the parietal pleura
lining the thoracic cavity during respiratory
 Volume :
 Mean amount of fluid in right pleural space in normal
individual is 8.4 +/- 4.3 ml.
 Normally the volume of fluid in right and left pleural
space is equal.
 Thickness :
 Pleural space slightly more narrow near the top(18.5mm)
than at bottom(20.3mm).
 pleural space width in the most dependent recess such
as costodiaphragmatic recess reaches 1 to 2 mm.
 Cells :
 Mean WBC count – 1,716 cells/mm3
 Mean RBC count – 700 cells/mm3
 Macrophages – 75 %
 Lymphocytes – 25 %
 Mesothilial, neutrophils, eosinophils ( < 2 % each )
Eosinophil > 10 % -- drug reaction, asbestosis, parasitic
infection, churg-strauss syndrome.
 Physiochemical factors :
• Protein – pleural fluid is similar to that of serum except
that low molecular weight protien such as albumin
present in relatively greater quantities in plural fluid.
• Ions :
Bicarbonates : increase by 20-25% to that in plasma.
Sodium : reduce by 3-5% to that in plasma
Chloride : reduce by 6-9% to that in plasma
Potassium : nearly identical to that in plasma
• Glucose : similar to that in plasma
• Less than 60 mg/dl – parapneumonic effusion, malignancy,
TB, RA, parasitic infection, churg-strauss syndrome.
• Pco2 : same as the plasma Pco2
• pH : due to elevated pleural fluid bicarbonate the
pleural fluid is alkaline with respect to plasma pH.
• Apperance : normally light yellow and clear
Underlying disaese
Pale yellow
Inflammatory exudates
Trauma, malignancy
Milky fluid
Amoebic liver abcess
Fungal infection
Yellow to green
Rheumatoid pleurisy
Pleural Fluid Formation
 Sources
 pleural capillaries,
 interstitial spaces of the lung,
 intrathoracic lymphatics,
 intrathoracic blood vessels,
 peritoneal cavity.
Pleural Capillaries
 The movement of fluid between the pleural capillaries
and the pleural space governed by Starling's law of
transcapillary exchange.
[Q]f - liquid movement
Lp - filtration coefficient/unit area or hydraulic water
conductivity of the membrane
A - surface area of the membrane
Pcap and pcap - hydrostatic and oncotic pressures of capillary
Ppl and ppl - hydrostatic and oncotic pressures of pleural space
sd - solute reflection coefficient for protein,
Parietal Pleura
 gradient for fluid formation is normally present.
 Hydrostatic pressure
 hydrostatic pressure of capillaries in parietal pleura is 30
cm of H2O
 Pleural pressure is -5 cm of H2O
 Net hydrostatic pressure = 30 – (-5) = 35 cm of H2O
 Oncotic pressure :
 Oncotic pressure in plasma = 34 cm of H2O
 Oncotic pressure in pleural space = 5 cm of H2O
 Net oncotic pressure = 34-5 = 29 cm of H2O
 Net gradient = 35-29 = 6 cm of H2O
 This gradient favours the movement of fluid from
capillaries in parietal pleura to the pleural space.
Visceral pleura
 Pressure in the visceral pleural capillaries is
approximately 6 cm of H2O less than that in the
parietal pleural capillaries.
 Filtration coefficient for the visceral pleura is less than
that of parietal pleura, because the capillaries in the
visceral pleura are much further from the pleural space
than those in parietal pleura.
 Thus, net gradient for fluid movements across the
visceral pleura is close to zero.
 It acts as a source of pleural fluid formation in
Pulmonary edema
Lung transplantation
Pulmonary embolisation
 Movement of fluid from interstitial to pleural space is
closely related with pulmonary venous pressure than
with the systemic venous pressure.
Peritoneal cavity
 Act as a source of pleural fluid formation in
Hepatic hydrothorax
Meig’s syndrome
Peritoneal dialysis
 Pressure in the pleural cavity is less than that of
peritoneal cavity
Thoracic duct/Blood vessel
 Thoracic duct injury :
 lymph will accumulate in pleural space producing
 Rate of fluid accumulation can be more than
 Blood vessel injury :
 Trauma of the blood vessels leading to blood
accumulation in pleural space cause hemothorax.
Pleural fluid absorption
 Lymphatic clearance :
 Pleural space is in communication with lymphatic
vessels in the parietal pleura by stomas in parietal
 Stomas are not present in visceral pleura
 Proteins, cells and all other particulate matter are
removed from the pleural space by this lymphatics in
parietal pleura.
 More fluid formation across the parietal pleura over
the ribs compared with intercostal spaces.
 Pleural fluid absorption more over intercostal spaces
than over ribs.
 More fluid formation over the caudal ribs than over
the cranial ribs.
 Increase in breathing frequency results in more fluid
Pleural effusion
 Pleural effusion is excess fluid that accumulates
between the two pleural layers, the fluid-filled space
that surrounds the lungs.
 It occurs when the rate of pleural fluid formation
exceeds the rate of pleural fluid absorption.
 Normal rate of pleural fluid formation – 0.01 ml/kg/hr
 Normal rate of pleural fluid absorption – 0.01 ml/kg/hr
but it can exceed upto 0.20 ml/kg/hr
 Increased pleural fluid formation
 Increased interstitial fluid in the lung (most common)
Left ventricular failure, pneumonia, and pulmonary embolus
Increased intravascular pressure in pleura
 Right or left ventricular failure, superior vena caval syndrome
Increased permeability of the capillaries in the pleura
 Pleural inflammation
 Increased levels of vascular endothelial growth factor
Increased pleural fluid protein level
Decreased pleural pressure
 Lung atelectasis or increased elastic recoil of the lung
Increased fluid in peritoneal cavity
 Ascites or peritoneal dialysis
Disruption of the thoracic duct
Disruption of blood vessels in the thorax
 Decreased pleural fluid absorption
 Obstruction of the lymphatics draining the parietal
 Elevation of systemic vascular pressures
 Superior vena caval syndrome or right ventricular
 Disruption of the aquaporin system in the pleura
Transudative vs exudative
 Transudative –
Pulmonary embolism
Nephrotic syndrome
Peritoneal dialysis
SVC syndrome
 Exudative :
Connective tissue disease
Drug reaction
Exudative effusion
 Light’s criteria [satisfying anyone criterion means it is
 Pleural total protein/serum total protein > 0.5
 Pleural LDH/serum LDH > 0.6
 Pleura LDH > 2/3 of the upper limits of normal for
serum LDH
 For patients with high suspicion for transudative, but
meets light’s criteria –
Serum albumin – pleural albumin < 1.2 gm/dl confirm the
effusion is exudative.
Therapeutic uses of pleural space
 Intrapleural gene transfer :
 Easy accessibility
 Large surface area
 Ability to provide high concentration of secreted gene
products to chest structure
 Low risk of vector induced inflammation
 Treatment of accidental hypothermia
Clinical conditions associated with pleura
• Pleuritis or pleurisy : This is the inflammation of the
pleura. Acute pleuritis is marked by sharp, stabbing pain,
especially on exertion.
Pneumothorax : Presence of air in the pleural cavity.
Entry of air into the pleural cavity, resulting from a
penetrating wound of the parietal pleura or rupture of a
lung results in partial collapse of the lung.
Hemothorax : Presence of blood in the pleural cavity. It
results more often from injury to a major intercostal
vessel than laceration of lung.
Hydropneumo thorax : prence of both fluid and air in
the pleural cavity.
Empyema : presence of pus in pleural cavity.